A cushion constituting the seat proper of a seat is usually made of a deformable material such as a foam and is defined by a top, by flanks, and by a bottom that is carried by a frame. A cover of flexible material is fitted on the foam, e.g. a loose cover. The cover itself comprises a panel, a skirt, and a margin that extend mutually one from the other, and when the cover is in position on the cushion, they extend respectively over the top of the cushion, over at least a major portion of the flanks of the cushion, and over a corresponding marginal band around the bottom of the cushion. As a result, the cushion and its frame are enclosed between the panel and the margin of the cover.
To keep the margin in place over the bottom of the cushion and the frame, the free edges of the margin are generally provided with rigid rods that co-operate with complementary means carried by the frame.
An object of the invention is to provide a method and a cover for covering a cushion that avoids the need to provide such assembly rods around the outline defined by the free edges of the margin. For a manufacturer mass producing seats, this represents a considerable reduction in the number of parts and in assembly time.
Proposals have already been made in European patent EP-0 223 312 to hold the margin the cover in place on the bottom and the frame of the cushion by means of a tensioning thread passed along a channel sewn along the free edge of the margin. Once the cover has been placed on the cushion, the thread is tensioned by pulling on its ends, thereby shortening the thread and thus urging the margin against the bottom of the cushion. The free edge of the margin is under tension and is gathered along its entire length.